Chromatically corrected objective with specifically structured and arranged dioptric optical elements and projection exposure apparatus including the same

Abstract

An objective having a plurality of optical elements arranged to image a pattern from an object field to an image field at an image-side numerical aperture NA>0.8 with electromagnetic radiation from a wavelength band around a wavelength λ includes a number N of dioptric optical elements, each dioptric optical element i made from a transparent material having a normalized optical dispersion Δ n i =n i (λ 0 )− n i (λ 0 +1 pm) for a wavelength variation of 1 pm from a wavelength λ 0 . The objective satisfies the relation  ∑ i = 1 N ⁢ Δ ⁢ ⁢ n i ⁡ ( s i - d i )  λ 0 ⁢ NA 4 ≤ A for any ray of an axial ray bundle originating from a field point on an optical axis in the object field, where s i is a geometrical path length of a ray in an ith dioptric optical element having axial thickness d i and the sum extends on all dioptric optical elements of the objective. Where A=0.2 or below, spherochromatism is sufficiently corrected.

What is claimed is: 
     
       1. An objective comprising:
 a plurality of optical elements arranged to image a pattern from an object field in an object surface of the objective to an image field in an image surface region of the objective with electromagnetic radiation emitted from a radiation source and having a wavelength band centered on a wavelength λ, where λ<260 nm and a band width of the radiation is greater than 0.5 pm, 
 wherein the objective exhibits a longitudinal spherical aberration SPH that varies within the wavelength band such that: 
 (SPH 2 −SPH 1 )/Δλ<0.2 mm/nm, 
 where SPH 1  is the longitudinal spherical aberration at λ−Δλ 
 and SPH 2  is the longitudinal spherical aberration at λ+Δλ, and 
 wherein the objective has an image-side numerical aperture NA>0.8. 
 
     
     
       2. The objective as claimed in  claim 1 , wherein (SPH 2 −SPH 1 )/Δλ<0.15 mm/nm. 
     
     
       3. The objective as claimed in  claim 1 , wherein (SPH 2 −SPH 1 )/Δλ<0.06 mm/nm. 
     
     
       4. The objective according to  claim 1 , wherein the optical elements form:
 a first objective part configured to image the pattern from the object surface into a first intermediate image, and having a first pupil surface; 
 a second objective part configured to image the first intermediate image into a second intermediate image, and having a second pupil surface optically conjugate to the first pupil surface, and 
 a third objective part configured to image the second intermediate image into the image surface, and having a third pupil surface optically conjugate to the first and second pupil surfaces. 
 
     
     
       5. The objective according to  claim 4 , wherein:
 the optical elements are arranged along an optical axis, 
 the second objective part includes a single concave mirror optically close to the second pupil surface, 
 a first folding mirror is arranged optically close to the first intermediate image to reflect radiation coming from the object surface toward the concave mirror and 
 a second folding mirror is arranged optically close to the second intermediate image to reflect radiation coming from the concave mirror toward the image surface. 
 
     
     
       6. The objective according to  claim 4 , wherein the second objective part includes a concave mirror having a reflective mirror surface positioned at or close to the second pupil surface and a lens group with negative refracting power immediately in front of the concave mirror and coaxial with the concave mirror and passed twice by the electromagnetic radiation. 
     
     
       7. The objective according to  claim 4 , wherein an aperture stop defining an effective image side numerical aperture NA of the objective is arranged at the first pupil surface or at the second pupil surface. 
     
     
       8. The objective as claimed in  claim 1 , wherein the objective has an image-side numerical aperture NA≥1.35. 
     
     
       9. The objective as claimed in  claim 1 , wherein the objective is configured as an immersion objective with an image-side numerical aperture NA≥1 when used in conjunction with an immersion liquid in an image-side working space between an exit surface of the objective and the image surface during operation. 
     
     
       10. The objective as claimed in  claim 1 , wherein the objective has an immersion lens group having a convex object-side entry surface bounding at a gas or vacuum and an image-side exit surface in contact with an immersion liquid in operation, wherein the immersion lens group is at least partly made of a high-index material with refractive index n≥1.6 at the wavelength λ. 
     
     
       11. The objective as claimed in  claim 10 , wherein the immersion lens group is a monolithic plano-convex lens made of the high-index material. 
     
     
       12. The objective as claimed in  claim 11 , wherein the high-index material is chosen from the group consisting of aluminum oxide (Al 2 O 3 ), beryllium oxide (BeO), magnesium aluminum oxide (MgAlO 4 , spinell), yttrium aluminium oxide (Y 3 Al 5 O 12 ), yttrium oxide (Y 2 O 3 ), lanthanum fluoride (LaF 3 ), lutetium aluminium garnet (LuAG), magnesium oxide (MgO), calcium oxide (CaO), and lithium barium fluoride (LiBaF 3 ). 
     
     
       13. A projection exposure apparatus configured to expose a radiation sensitive substrate arranged in a region of an image surface of a projection objective with at least one image of a pattern of a mask that is arranged in a region of an object surface of the projection objective, comprising:
 a radiation source emitting ultraviolet radiation from a wavelength band around a wavelength λ; 
 an illumination system receiving the radiation from the radiation source and shaping illumination radiation directed onto the pattern of the mask; and 
 an objective according to  claim 1 , 
 wherein the wavelength λ<260 nm and the band width of the radiation is greater than 0.5 pm.